Solar energy has received recent interest as an alternative to fossil fuels. Nonetheless, the design of collectors converting such energy to a useful form has created a controversey not yet resolved.
One type of solar collector covers an area, such as the roof of a building, with appropriate transducers. The rays striking these transducers undergo conversion into heated fluids or electricity as appropriate.
However, the elements effecting the conversion of solar energy can efficiently utilize vastly greater amounts of light than that ever received directly from the sun. Moreover, these elements represent relatively expensive items in the system. Consequently, their use for only that radiation naturally incident upon their surfaces appreciably increases the cost and lowers the desirability and utilization of such collectors.
Thus, to improve the economics of the collectors, many designers have increased the concentration of radiation striking the transducing elements. Generally, they employ a focussing device which the rays strike prior to impinging upon the transducers. These inexpensive focusers amass the radiation striking their large surfaces and concentrate them to the appreciably smaller surface areas of the transducers. Thus, a relatively minor additional expense allows the transducers to produce a several-fold greater amount of useful energy.
However, the use of focussing elements requires a precise spatial orientation between the sun, the transducers and the element themselves. Relatively minor displacements from the required alignment produce precipitous declines in the system's efficiency. Moreover, as the earth rotates on its axis, the alignment between the various components will necessarily undergo these misalignments. In addition, the focussing elements that concentrate the solar rays with greatest efficiency suffer the greatest defocussing.
To allow use of focusers throughout the day, various manufacturers have incorporated tracking devices into their systems. These have generally taken the form of electric motors coupled to sensing devices. The motors move the focussing elements and transducers to a position where the sensing devices detect a maximum of solar energy in the region of the latter.
These systems, however, suffer drawbacks seriously limiting their desirability. The inclusion of a sensor, motor, and intermediate couplings significantly increases the cost of the system. Moreover, it requires a source of electricity plus the expenditure for its use.
Moreover, a heavily overcast day may cause the sensor-motor combination to gyrate uncontrollably while seeking the sun's rays. High winds may exceed the corrective capacity of the motor and simply blow the collector away from the requisite orientation.
More recent devices have compromised between the moving-focussing and the stationary-cell systems. These newer devices use stationary focussing elements. Their overall configuration, however, achieves some focussing throughout the day. Consequently, the devices produce better results than the stationary nonfocussing systems consisting of solar-cell arrays. Yet, their efficiencies never approach those of the sun-tracking collectors.